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    SubjectRe: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest]
    Andrea Arcangeli <andrea@suse.de> wrote:
    >
    > It's the readahead in my tree that allows the reads to use the max scsi
    > command size. It has nothing to do with the max scsi command size
    > itself.

    Oh bah.

    - *max_ra++ = vm_max_readahead;
    + *max_ra = ((128*4) >> (PAGE_SHIFT - 10)) - 1;


    Well of course that will get bigger bonnie numbers, for exactly the reasons
    I've explained. It will seek between files after every 512k rather than
    after every 128k.

    > You can wait 10 minutes and still such command can't grow. This is why
    > claiming anticipatory scheduling can decrease the need for readahead
    > doesn't make much sense to me, there are important things you just can't
    > achieve by only waiting.
    >

    The anticipatory scheduler can easily permit 512k of reading before seeking
    away to another file. In fact it can allow much more, without requiring that
    readhead be cranked up.

    -
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